Field of the Invention
The invention relates to a process and system for reduction of chemical oxygen demand, herein referred to as COD, and more particularly to a process and system that immobilizes select microorganisms in a stable biofilm on an adsorbent medium, such as on a granular activated carbon carrier filled in a reactor.
Description of Related Art
Wastewater from an industry may be organic or inorganic in nature or a combination of both. In most cases, it contains toxic ingredients, which can pose a direct threat to human being and animals. Another direct effect of wastewater pollution is to deplete, through the excessive organic load, the dissolved oxygen (DO) content of receiving waters to the point that the stream becomes incapable of exercising the self-purification processes. The deoxygenation may be high enough to practically destroy all fish and other aquatic life. The problem is compounded by the fact that solubility of oxygen in water is very low, less than 12 mg/l. This oxygen comes from two sources, viz. diffusion from the atmosphere at the air/water interface and as a by-product of photosynthesis. Photosynthetic organisms, such as plants and algae, produce oxygen when there is a sufficient light source. During times of insufficient light, these same organisms consume oxygen, resulting in the depletion of DO levels.
Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) are indices of the biologically degradable and chemically oxidizable fractions of the wastewater, respectively. COD of the treated effluent is representative of the effectiveness of a treatment technique in its ability to remove the total organic material present in the influent. These parameters are frequently used to define influent and effluent characteristics and also ensure the wastewater treatment efficiency.
Recalcitrant COD refers to organic compounds that resist microbial degradation (bio-refractory) or are not readily biodegradable. Existing biological treatment technologies including the activated sludge process, biological filtration or membrane bioreactors (MBR) cannot efficiently remove these recalcitrant COD compounds. Adsorption and oxidation may be able to remove or destruct these organic compounds, but the cost is often very high. It is accordingly desired to improve methods of removing recalcitrant organic pollutants.